Steel is an iron carbon alloy with a carbon content between 0.04% and 2.3%. To ensure its toughness and plasticity, the carbon content generally does not exceed 1.7%. The main elements of steel include silicon, manganese, sulfur, phosphorus, etc. in addition to iron and carbon. There are various classification methods for steel, and the main methods are as follows: 1. Classified by quality (1) Ordinary steel (P ≤ 0.045%, S ≤ 0.050%) (2) High quality steel (both P and S ≤ 0.035%) (3) High quality steel (P ＜ 0.035%, S ≤ 0.030%) 2. Classification by chemical composition 1) Carbon steel: a. Low carbon steel (C ≤ 0.25%); b. Medium carbon steel (0.25 ＜ C ≤ 0.60%); c. High carbon steel (C>0.60%). 2) Alloy steel: a. Low alloy steel (total alloy element content ≤ 5%) b. Medium alloy steel (total alloy element content 5-10%) c. High alloy steel (total alloy element content>10%). 3. Classification by forming method: (1) Forged steel; (2) Cast steel; (3) Hot rolled steel; (4) Cold drawn steel. 4. Classification by metallographic structure (a scientific study of the internal microstructure of steel) 1) A. Hypoeutectoid steel (ferrite+pearlite) in annealed state. b. Euectoid steel (pearlite). c. Hypereutectoid steel (pearlite+cementite). d. Lainitic steel (pearlite+cementite). 2) Normalized state: a. Pearlite steel; b. Bainite steel; c. Martensitic steel; d. Austenitic steel. 3) Without or partially undergoing phase transition 5. Classified by purpose 1) Construction and engineering steel: a. Ordinary carbon structural steel; b. Low alloy structural steel; c. Reinforced steel. 2) Structural steel: a. Steel for mechanical manufacturing: (a) Quenched and tempered structural steel; (b) Surface hardened structural steel: including carburized steel, ammonia steel, and surface quenched steel; (c) Easy to cut structural steel; (d) Cold plastic forming steel: including cold stamping steel and cold heading steel. b. Spring steel c. Bearing steel 3) Tool steel: a. Carbon tool steel; b. Alloy tool steel; c. High speed tool steel. 4) Special performance steel: a. Stainless and acid resistant steel; b. Heat resistant steel includes antioxidant steel, heat strength steel, and valve steel; c. Electric heating alloy steel; d. Wear resistant steel; e. Low temperature steel; f. Electrical steel 5) Professional steel - such as steel for bridges, ships, boilers, pressure vessels, agricultural machinery, etc. 6. Comprehensive classification 1) Ordinary steel: a. Carbon structural steel: (a) Q195; (b) Q215 (A, B); (c) Q235 (A, B, C); (d) Q255 (A, B); (e) Q275. b. Low alloy structural steel. c. Ordinary structural steel for specific purposes 2) High quality steel (including high-grade high-quality steel) a. Structural steel: (a) High quality carbon structural steel; (b) Alloy structural steel; (c) Spring steel; (d) Easy to cut steel; (e) Bearing steel; (f) High quality structural steel for specific purposes. b. Tool steel: (a) Carbon tool steel; (b) Alloy tool steel; (c) High speed tool steel. c. Special performance steel: (a) Stainless and acid resistant steel; (b) Heat resistant steel; (c) Electric heating alloy steel; (d) Electrical steel; (e) High manganese wear-resistant steel. 7. Classification by smelting method 1) Classified by furnace type a. Open hearth steel (using air as an oxidant): (a) acidic open hearth steel; (b) Alkaline open hearth steel. b. Converter steel (using oxygen as an oxidant): (a) Acidic converter steel; (b) Alkaline converter steel. Or (a) bottom blown converter steel; (b) Side blown converter steel; (c) Top blown converter steel. c. Electric furnace steel (refining high-quality steel): (a) Electric arc furnace steel; (b) Electric slag furnace steel; (c) Induction furnace steel; (d) Vacuum consumable furnace steel; (e) Electron beam furnace steel. 2) Divided by degree of deoxidation and pouring system: a. Boiling steel (incomplete degree of deoxidation); b. Semi killed steel (deoxygenation degree between boiling steel and killed steel); c. Killed steel (with a relatively complete degree of deoxidation); d. Special killed steel (with the most complete degree of deoxidation and high quality of steel). 8. Classified by appearance: divided into four categories: a. profiles, b. plates, c. pipes, and d. metal products. a. Profile: Heavy rail: Steel rails weighing over 30 kilograms per meter (including crane rails); Light rail: a steel rail with a weight of less than or equal to 30 kilograms per meter. Large, medium, and small section steels: ordinary round steel, square steel, flat steel, hexagonal steel, I-beam, channel steel, equal and unequal angle steel, and threaded steel, etc. Wire: Round steel and wire rods with a diameter of 5-10 millimeters. Cold formed steel: a type of steel formed by cold bending steel or steel strips. High quality profiles: High quality round steel, square steel, flat steel, hexagonal steel, etc. b. Sheet metal; Thin steel plate: A steel plate with a thickness of 4 millimeters or less. Medium and thick steel plates: Steel plates with a thickness greater than 4 millimeters. Middle plate: thickness greater than 4mm but less than 20mm); Thick plate: thickness greater than 20mm but less than 60mm; Extra thick plate: with a thickness greater than 60mm. Steel strip: also known as strip steel, it is actually a thin steel plate that is long and narrow and supplied in coils. Electrical silicon steel sheet: also known as silicon steel sheet or silicon steel sheet. c. Pipe material: Seamless steel pipe: a seamless steel pipe produced by methods such as hot pressing, cold rolling (cold drawing or extrusion), etc. Welded steel pipe: a steel pipe made by bending a steel plate or strip into shape and then welding it. d. Metal products: including steel wires, wire ropes, steel strands, etc.